Electrical apparatus



June 2, 1931. BYRNES 1,808,524

ELECTRICAL APPARATUS Filed July 19. 1927 Figl mfg TE I i. 3 W35 35;? 6ii RADIO Audio Inventor: :[hving F. Bynnes,

His Attorney Fatent ed June 2, 1931 UNITED STATES PATENT OFFICE IRVINGF. BYRNES, OF SCHENEGTADY, NEW YORK, ASSIGNOR 'IO GENERAL ELECTRICCOMPANY, A CORPORATION OF; NEW. YORK ELECTRICAL APPARATUS I Applicationfiled July 19, 1927. Serial No. 206,968.-

My invention relates to electrical apparatus comprising means foreliminating currents of undesired frequencies, and has for its principalobject the provision of an improved wave filter which offers a highattenuation to currents of undesired frequencies, possesses sharp cutoffand operates with a high degree of efficiency.

Various types of wave filters comprising capacities and inductancesinterconnected with one another have been provided in the past. Theoperation of many of these filters involves considerable power lossesand is unsatisfactory in other respects, such as the sharpness of thecutoff and the attenuation offered to the currents of the undesiredfrequencies. In accordance with my invention, these difliculties areavoided by the provision of a filter which comprises a piezo electricelement such as a crystal of quartz or the like.

My invention will be better understood from the following descriptionwhen considered in connection with the accompanylng drawings and itsscope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 shows a modulating system wherein myinvention has been embodied; Fig. 2 shows a filter of the low frequencypass type; Fig. 3 shows a filter of the high frequency pass type; andFig.

4 shows the application of my invention to a frequency band eliminator.

The system illustrated by Fig. 1 comprises a pair of balanced modulationdevices which l and 2 from a source 11; and the negative grid biaspotential required for proper operation of the devices 1 and2 is appliedto the input-circuit by a source 12. V

The crystal 8 is a small block of quartz, or

other suitable piezo electric material, provided with surfaces that arelocated in known relation to its optical and electrical axes. The freevibration of this crystal is determined for the most part by itsmechanical dimensions. Whensub-jected to anelectrostatic field of afrequency corresponding to its free vibrationperiod, the crystalexhibits the properties of a resonant circuit having extremely lowlosses. With the crystal 8. connected as illustrated in Fig. 1, currentsof frequencies which correspond. substantially to its free vibrationperiod are excluded; from the output circuit 3 and a sharp line ofdemar-cation is readily maintained between the transmitted and excludedfrequencies.

.Figs. -2 to 4 illustrate the use of, a piezo electric element invarious types of filters. Thus 2 shows the use of the piezo electricelement in a low frequency pass type of filter comprisingseries-connected inductances 13 and 14; Fig. 3 shows the use of theelement in a high frequency pass type of filter comprisingseries-connected capacities 15 and 16; and Fig. 4 shows the use of theelement in a frequency band eliminator type of filter comprisingseries-connected inductances 17 and 18 and capacities 19 and 20 whichare connected in parallel with the inductances 17 and 18 respectively.In each embodiment of the invention, the piezo electric element isconnected in shunt to the va rious other elements of the filter.Numerous tests have shown that a filter comprising a piezo electricelement connected in this manner possesses the advantages of low loss,sharp cutoff and high attenuation for the frequencies which come withinthe range determined by the mechanical dimensions of the crystal.

The embodiment of the invention illustrated and described herein hasbeen selected for the purpose of clearly setting forth the prin ciplesinvolved. It will be apparent, however, that the invention issusceptible of beencountered in its use and I therefore aim mg modifiedto meet the different conditions to cover by the appended claims allmodifications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. The combination of a circuit, means for energizing said circuit, anda filter comprising a pair of impedance devices'connected in series withsaid circuit, anda piezo electric element which is connected in shunt tosaid circuit at a point intermediate said devices, said element having afree vibration period corresponding to the frequencies ofthe currents tobe excluded from said circuit.

2. The combination of a circuit, a pair of inductances connected inseries with said circuit and a piezoelectric element connected in shuntto said circuit at' 'a point intermediate said inductances, said elementhaving a free vibration period corresponding to the frequencies of thecurrents which are to be excluded from said circuit.

3 The combination of a circuit, a pair'of inductances and a pair ofcapacities connect.- ed in series .with said circuit, and a piezoelectric element connected in shunt to said circuit at a .pointintermediate said induc tances, said element having a free vibrationperiod corresponding to the frequencies of the currents Which are to beexcluded from said circuit.

In witness whereof, I have hereunto set my hand this'18th day of July,1927.

" IRVING F. BYRNES.

